Mounting machines for the mounting of semiconductor chips are known in the field as die bonders. The mounting machine is used to mount the numerous uniform chips of a wafer which are situated adjacent to one another on a chip carrier one after the other on a substrate, e.g. a metallic lead frame. The die bonder comprises a wafer table on which the chip carrier is situated, a transport system for supplying the substrate and a pick-and-place system in order to remove the semiconductor chips from the chip carrier and place them on the substrate. The pick-and-place system comprises a bonding head with a chip gripper which is moved back and forth by a drive system. The chip gripper is rotatable about a vertical axis, so that the rotational position of the semiconductor chips can be changed if necessary. The chip gripper comprises an exchangeable gripping member, which is a suction member to which vacuum may be applied, which is known in the field as a “pick-up tool” or “die collet”.
Extremely high demands are placed on mounting machines of this kind. They need to be placed in a precise position on the substrate for further processing of the mounted chips. Two cameras are provided on the die bonder to ensure that the semiconductor chips can be placed on the substrate with a precision that lies in the micrometer range. The first camera measures the position of the semiconductor chip to be picked up by the chip gripper and supplies the positional data which relate to a first system of coordinates. The second camera measures the position of the substrate place on which the semiconductor chip needs to be placed and supplies positional data that relate to a second system of coordinates. The pick-and-place system controls the bonding head on the basis of the information supplied by the cameras in such a way that the chip gripper can remove the semiconductor chip from the wafer table and can place the same in a precise positional way at the correct location on the substrate place. The position of the pick-and-place system relates to a third system of coordinates which is independent of the system of coordinates of the camera.
During operation of the die bonder, the problem arises that the relative position of the three systems of coordinates may change due to different conditions. The temperature at different locations of the die bonder often changes, intentionally or unintentionally. This mostly leads to the consequence that the conversion of target coordinates which were determined in the system of coordinates of the first camera or in the system of coordinates of the second camera into motional coordinates for the pick-and-place system is no longer as exact as required.